Anaphylaxis is an acute allergic reaction or hypersensitivity response that may be fatal within minutes and is a medical emergency. Eighty to ninety percent of cases involve sudden-onset cutaneous changes (pruritus, flushing, hives, and swelling of mouth, lips, and tongue). These skin findings may present with sudden onset of respiratory compromise or sudden drop in blood pressure with end-organ symptoms, and often present in a person with no prior history of severe reaction. Gastrointestinal (GI) symptoms indicate a likely allergen exposure. Other signs and symptoms include headache, periorbital edema, hypoxemia, dyspnea, hypotonia, tachycardia, altered mental state, wheezing, nausea, and vomiting.

Foods and additives, inhalants, insect stings, and medications may be triggers. Pathogenesis involves systemic activation of mast cells and basophils resulting in the release of inflammatory mediators. This activation may be immunoglobulin E (IgE) (in the case of classical anaphylaxis) or non-IgE mediated (anaphylactoid reaction). In adults, multiple episodes of anaphylaxis (eg, related to drugs) should lead to a consideration of mastocytosis.

Anaphylactoid reactions mimic anaphylactic reactions and cannot be distinguished clinically aside from the fact that anaphylaxis is IgE mediated and as such requires patient sensitization of the offending trigger. Anaphylactoid reactions are not IgE mediated and occur without sensitization, as the offending trigger causes direct mast cell and basophil activation.

Delayed diagnosis and treatment predict poor prognosis. Immediate management involves removal of the triggering allergen if possible, epinephrine by intramuscular injection, and further evaluation and management.

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